Cohesion (geology)

Cohesion is the component of shear strength of a rock or soil that is independent of interparticle friction.

In soils, true cohesion is caused by following:

1. Electrostatic forces in stiff overconsolidated clays (which may be lost through weathering)
2. Cementing by Fe₂O₃, CaCO₃, NaCl, etc.

There can also be apparent cohesion. This is caused by:

1. Negative capillary pressure (which is lost upon wetting)
2. Pore pressure response during undrained loading (which is lost through time)
3. Root cohesion (which may be lost through logging or fire of the contributing plants, or through solution)

Typical values of cohesion

Cohesion (alternatively called the cohesive strength) is typically measured on the basis of Mohr–Coulomb theory. Some values for rocks and some common soils are listed in the table below.

References

• Collins internet-linked dictionary of Geology

See also

• Mohr–Coulomb failure criterion